Railway braking apparatus



F 1932- J. w. LIVINGSTON RAILWAY BRAKING APPARATUS Filed April 22, 1931 To Soump 0i Fluid Pressure BY Qafllaz M ATTORNEY.

Patented Apr. 26, 1932 UNITED S'i'TES PATENT OFFICE JOHN VT. LIVINGSTON, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO THE UNION SWITCH & SIGNAL COMPANY, OF SW'ISSVALE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA RAILWAY BRAKING APPARATUS Application filed April 22,

My invention relates to railway braking apparatus, and particularly to braking apparatus of the type comprising a braking bar located in the trackway and actuated by a iiuid pressure motorcontrolledfrom a remote point.

I will describe one form of railway braking apparatus embodying my invention, and will then point out the novel features thereof in the claim.

The accompanying drawing is a view, partly diagrammatic, and partly cross-sectioned, illustrating one form of apparatus embodying my invention.

Referring to the drawing, the reference characters 1 and 1 designate the track rails of a stretch of railway track. Located on opposite sides of rail 1 and extending parallel therewith are two braking bars 2 and 8. Two similar braking bars 2 and 3 extend parallel with rail 1 on opposite sides thereof.

The braking bars a, 3, 2 and 8 are operated by a fluid pressure motor M, which, in the form here shown, comprises a cylinder 4 containing an auxiliary piston 6 which is movable between the left-hand end of the cylinder and an intermediate point in the cylinder, and a main piston 5 which is movable between the right-hand end of the cylinder and the auxiliary piston 6. It will be plain, therefore, that when the auxiliary piston 6 occupies its projected position, in which it is illustrated in the drawing, the stroke of the main piston 5 is less than when the auxiliary piston 6 occupies its retracted position. The sealing ring of the auxiliary piston 6 is located at 6 in the drawing, and the parts are so proportioned that even when the auxiliary piston occupies its projected position, it does not blank a pipe 28 which communicates with the side of the cylinder l. Piston 6 is provided with flutes or holes by means of which the pipe 28 may at all times communicate with the region between the. pistons 5 and 6. The main piston 5 of motor M is operatively connected withrthe braking bars 2, 3, 2 and 3 by means of suitable operating mechanism, one form of which I'will now describe.

As here shown, this operating mechanism comprises a link 8 which is connected at one 1931. Serial No. 532,011.

end to the free end of the piston rod 7, and

at the other end to a lever 9 which is pivotally 9 constitute a toggle by means of which the cranks 12 and 15 may be swung in the same directions when the piston. 5 of motor Mis operated. The freeend of crank 12 is operatively connected with the braking bars 2 and 2 respectively, by means of resilient connections which include springs 17 and 18, and, similarly, the free end of the crank15 is operatively connected with the braking bars 3 and 3? by means of resilient connections which include springs 19 and 20. It will be seen, therefore, that when piston'5 moves toward the left, the cranks 12 and 15 i are both swung in a clockwise direction, so that each braking bar is moved toward the associated rail into a braking position in which it engages the side of a wheel of a rail-, way car traversing the rails l and 1 vVhen the piston5 moves toward the right,

however, the cranks 12 and 15 are swungin;

a counter-clockwise directiomand thebrakmg bars are moved away from the associated rails to their non-braking positions, in l which they are out of engagement with the wheels of a passing car. One form of operating mechanism of the type described is disclosed .and claimed in the copending application for Letters Patent of the United States, Serial No. 307,895, filed by Herbert L., Bone, on Sept. 24:, 1928, for. railway braking apparatus.

The motor M is controlled by four magnet valves V V V and V As hereshown, each valve V comprises a valve stem 21, biased to an upper position by a spring 22, and provided with an armature 23 and a winding 24:. lVhen valve V is energized, valve stem 21 of this valve moves downwardly against the bias exerted by spring 22, and a pipe 26,

which communicates with the region of cylf inder 4 between the auxiliary piston 6 and the adjacent end of the cylinder, is then connected with a pipe 25 which is constantly supplied with fluid pressure, usually air, from a suitable source not shown in the drawing. When valve V is deenergized, however, valve stem 21 is moved upwardly by spring 22, and pipe 26 is then disconnected from pipe 25. When valve V is energized, valve stem 21 of this valve moves downwardly, thereby connecting pipe 26 with pipe 28, but when valve V is deenergized, pipe 26 is disconnected from pipe 28. When valve V is energized, pipe 29 which communicates with the region of cylinder 4 between the main piston 5 and the adjacent end of the cylinder is vented to atmosphere through port 54, but when valve V is deenergized, pipe 29 is dis connected from atmosphere, and pipe 28 which is disconnected from port 54 when this valve is energized, is then connected with port 54. When valve V is energized, valve stem 21 of this valve moves downwardly and connects pipe 29 with pipe 25, but when valve V is deenergized, pipe 29 is disconnected from pipe 25. It will be apparent, therefore, that when valve V is energized and valve V is deenergized, the region in cylinder 4 between the auxiliary piston 6 and the left-hand end of the cylinder is supplied with fluid pressure; when valves V V and V are all energized, the regions in cylinder 4 between the pistons 5 and 6, and between the auxiliary piston 6 and the lefthand end of the cylinder, are both supplied with fluid pressure; and when valve V is deenergized, and valve V is energized, the region in cylinder 4 between piston 5 and the right-hand end of the cylinder is supplied with fluid pressure. Furthermore, when valves V and V are deenergized, and valve V is energized, the region between the auxiliary piston 6 and the left-hand end of the cylinder is vented to atmosphere; when valve V is deenergized, the region in cylinder 4 between the pistons 5 and 6 is vented to atmosphere; and when valve V is energized, the region in cylinder 4 between piston 5 and the right hand end of the cylinder is vented to atmosphere.

It will be noted that the pipe 26 which communicates with the cylinder 4 between the auxiliary piston 6 and the left-hand end of the cylinder is provided with a throttling restriction 27. The function of this restriction willbe explained in detail hereinafter.

The valves V V V and V are controlled in part by a plurality of circuit controllers wvhich are operated in accordance with the position of piston 5. As shown in Fig. 1, there are six of these circuit controllers designated by the reference characters S S S S S and S respectively. When the piston 5 occupies its extreme right-hand position in which it is shown in the drawing, so

that the braking bars are in their open or ineffective positions, contact 3839 of circuit controller 8*, contact 4041 of circuit controller S and contact 4243 of circuit controller S are all closed. As soon as piston 5 starts to move toward the left, contact 32- 33 of circuit controller S and contact 3485'= of circuit controller 5 become closed. Shortly before piston 5 reaches the position which: the braking bars just engage the wheels of a car in the braking apparatus contact 88-39 of circuit controller S opens, and immediate-- ly thereafter contact 40-41 of circuit controller S opens; and when the piston has reached the position in which the braking bars just engage the wheels of a car in the braking apparatus, contact 3637 of circuit controller S becomes closed. Upon slight additional movement of piston 5 toward the left, contact 4248 of circuit controller S opens, and just before piston 5 reaches the end of its stroke in this direction contact 42-43 of circuit controller S becomes closed.

The valves V are also controlled in part by a plurality of pressure responsive devices, each designated by the reference character P with a distinguishing exponent. Referring to the pressure responsive device P for example, this device comprises a Bourdon tube 44 connected, by means of a pipe 31, with pipe 28, and therefore subjected to the pressure in the region between the pistons 5 and 6 in 2 29 which communicates with cylinder 4 be tween the main piston 5 and the right-hand end of the cylinder. The devices P and P are arranged to operate in succession the pressure in the right-hand end of cylinder 4 increases. For example, for all pressures below ten pounds per square inch, contact 4545 of both of these devices is closed. If the pressure exceeds ten pounds per square inch, however, contact 45 45 of device P opens, and if the pressure exceeds twenty M pounds per square inch contact 45 45" of device 1 closes. In similar manner, the pressure responsive device P is adjusted to open its contact 4545 at forty pounds per square inch and to close its contact 45-45 at fifty pounds per square inch. Of course, these specific pressures are not essential, but are only mentioned for purposes of explanation.

The valves V are further controlled by The pressure re- The Bourdon tube 44 controls means of a manually operablelever L which, as here shown, is capable of assuming five as here shown, is capable of assuming live drawing, and designated by the reference characters p to 39 inclusive. The lever L operates two contact arms 46 and 46. The contact arm 46 is adapted to engage a selected one or ones of a plurality of fixed contacts designated by the reference characters 47'to 53, inclusive, and the contact arm 46 is similarly adapted to engage a plurality of fixed contacts designated by the reference characters 46 to 51, inclusive. The lever L is also provided with a segmentcontact 55 so disposed that when the contact arm 46 engages any one of the fixed contacts. 48, 49 or 50, the contact arm also engages the segment contact55, but that the contact arm 46 does not engage the segment contact 55 when it engages fixed contacts 47 or 51 The lever L will usually be located at a point remote from the braking apparatus, as in the control cabin of a classification yard car retarder system, and will be connected with the braking apparatus by means of line wires extending from the control cabin to the braking apparatus.

As shown in the drawing, lever L occupies its or off position, contact 46-47 of lever L is therefore closed, and a circuit is therefore completed for valve V over which current flows from a suitable source, such as a battery B, through line wire 56, wires 57 and 58, winding 24 of valve V wires 59 and 60, an asymmetric unit 61 in its low resistance direction, wire 62, line wire 63, wire 64, and contact 46-47 of lever L back to battery B. Valve V is therefore energized so that the region of cylinder 4 between piston 5 and the right-hand end of the cylinder is vented to atmosphere through pipe 29 and port 54 of valve V Valves V, V and V are all deenergized. The supply of fluid pressure to the regions of cylinder 4-between the pistons 5 and 6, and between the auxiliary piston 6 and the left-hand end of the cylinder is therefore cut off. The contacts 45-45 of the pressure responsive devices P are all closed and the contacts 45-45 are all open. Piston 5 of motor M occupies its extreme right-hand position in cylinder 4, and the braking bars therefore occupy their retracted or ineffective positions. Contact 32-33 of circuit controller 8 contact 34-35 of circuit controller S contact 36-37 of circuit controller S and contact 42-43 of circuit cont-roller S are therefore all open; and contact 38-39 of circuit controller 5 contact 40-41 of circuit controller S and contact 42-43 of circuit controller S are closed. The auxiliary piston 6 of motor M occupies its projected position, the piston being held in this position by the fluid which is trapped in the cylinder betweenthe piston and the left hand endof the cylinder as willbe explained more fully hereinafter. V

In explaining the operation of the apparatus, I will first assume that the operator wishes to make a comparatively light brake application. To do this, he moves lever L to its 10 position, thereby opening contacts 46-52 and 46-57 and closing contacts 46- 48 and 46 -55. The opening of contact 46-47 interrupts the circuit which was previously closed for valve V at this contact, and valve V therefore becomes deenergized, so that the region of cylinder 4 between the main piston 5 and the right-hand end of the cylinder becomes disconnected from atmos phere, and the region of cylinder 4 between the main piston 5 and the auxiliary piston 6 becomes connected with atmosphere. The closing of contact 46 -48 of circuit controller L completes a circuit for valve V and currentflows from a suitable source such as a battery C through wire 65, contact 46*- 48 of lever L, wire 66,1ine wire 67, Wire 68, asymmetric unit 69 in its low resistance direction, wire v7O, contact 38-39 of circuit controller S wire 71, winding 24 of valve V wires 72, 58 and 57 and line wire 56 back to battery G. Valve V therefore becomes energized, and connects pipe 29 with pipe 25, so that fluid pressure is now supplied to cylinder 4 between the piston 5 and the ri-ght-handend of the cylinder. This pressure drives piston 5 towa-rd the left, thereby moving the braking bars toward their braking positions. It should be noted that the pressure available to commence the movement of the braking bars may be built up to fullline pressure which may be of the order of one hundred pounds per square inch, so that the response of the apparatus is very rapid. Shortly after piston 5 starts to move toward the left, contact 32-33 of circuit controller S becomes closed, and a circuit is then completed for valve V which passes from battery C through wire 65, contact 46-55 of lever L, line wire63, wire 73, contact 45-45 of pressure responsive device P wire 74, con tact 32-33 of circuit controller S wire 75, winding 24 of valve V and line wire 56 back to battery 0. Valve V therefore also becomes energized, thus connecting pipe 26 with pipe 25. When pipe 26 is connected with pipe 25, fullline pressure is supplied to cylinder 4 between the auxiliary piston 6 and the left-hand end of the cylinder but, due to the throttling restriction 27 in the pipe 26, the rate at which this pressure can build up in the cylinder is limited to a value which precludes any possibility of shock to the piston 6 in case this piston does not occupy its.

full projected position for any reason at the time valve V becomes energized. When this pressure has once built up, it holds the auxiliary piston in its projected position, thereby, limiting. the stroke of the main piston 5,

as will be pointed out more fully hereinafter. Shortly before the main piston 5 has moved to the left far enough so that the braking bars are in a position corresponding to the working range of the apparatus, that is to say, in a position to engage the wheels of a car in the braking apparatus, contact 38-39 of circuit controller S opens and interrupts the circuit which was previously closed for valve V* at this contact. If the pressure in cylinder 4 between piston 5 and the right-hand end of the cylinder is then below ten pounds per square inch, a branch around contact 38* 39 of circuit controller S in the circuit for valve V will be completed at contact 45-45 of pressure responsive device P which branch may be traced from wire 70, through wire 76, contact 45-45 of pressure responsive device P and wires 78, 77, 92 and 79 to wire 71. Under these conditions, therefore, valve V will remain energized until the pressure in the right-hand end of cylinder 4 exceeds ten pounds per square inch, at which time contact 45-45 of pressure responsive device 1 will open and will interrupt this branch, so that valve V will become deenergized. It usually happens, iowever, that during the preliminary movement of piston 5, the pressure in the right-hand end of cylinder 4 exceeds twenty pounds per square inch so that contact 4545 of pressure respensive device P is open and contact 45- 45 is closed. Under these conditions, when piston 5 reaches the position at which contact 38-39 of circuit controller S opens, valve V becomes deenergized and cuts off the supply of fluid pressure to the right-hand end of cylinder 4. However, the fluid which has already been admitted to the right-hand end of cylinder 4 now expands, and piston 5 therefore continues to move toward the left a suilicient distance to close contact 3687 of circuit controller S When this contact becomes closed, if the pressure in the righthand end of cylinder 4-still exceeds twenty pounds per square inch, a circuit will be completed for valve V, and current will flow from battery C through wire 65, contact 46 48 of lever L, wire 66, line wire 67 wire 68, asymmetric unit 69 in its low resistance direction, wires 70 and 76, contact 45 45 of pressure responsive device P wires 93 and 80, contact 3687 of circuit controller S wires 81 and E9, winding 4 of valve V wires 58 and 57, and line wire 56 back to battery C. Valve V will therefore become energized and will connect pipe 29 with port 54. The right-hand end of cylinder 4 will then be exhausted to atmosphere until the pres sure in this end of the cylinder has been reduced below twenty pounds per square inch whereupon contact 4545 of pressure responsive device P will open and will deenergize valve V It will be apparent, therefore from the foregoing that, when lever L '404l of circuit controller S occupies its 221 position, piston 5 is urged toward the left by a pressure of between ten and twenty pounds per square inch. The movement of piston 5 toward the left under these conditions is limited by the auxiliary piston 6, which as pointed out hereinbefore is held in its projected position by fluid pressure which is admitted to the left-hand end of cylinder 4 as soon as contact 32-33 of circuit controller S becomes closed, and the parts are so proportioned that the movement of lever 9 caused by this movement of piston 5 does not bring the toggle of which lever 9 forms a part to its dead-center position. It follows, therefore, that if a car enters the braking apparatus, the brakin bars may be forced away from the rails, thereby transmitting the reaction of the wheels, through the operating mechanism, to the piston 5. As a result, the piston 5 may be moved slightly toward the right, thereby cushioning the brakaction of the apparatus against the volume of air in cylinder 4.

If the operator desires to make a more powerful brake application, he moves lever L to its 10 position in which contacts 46-49 and 46-55 are closed. The operation of the apparatus is then similar to that just described with the following exceptions. Valve V* is now initially energized over a circuit which includes contact 40-41 of circuit controller S and which passes from battery B through line wire 56, wires 57, 58 and 72, winding 24 of valve V wires 71 and 79, contact 40-41 of circuit controller S wire 82, asymmetric unit 83 in its low resistance direction, wire 84, line wire 67, wire 85, contact 46- 49 of circuit controller L, and wire 86 back to battery B. When piston 5 has moved to the position where contact 40-41 of circuit controller S opens, the circuit for valve V which was previously closed at this contact is interrupted, but if the pressure in the left-hand end of cylinder 4 is then below forty pounds per square inch, valve V will remain energized by virtue of a branch for this circuit which branch passes from wire 79, through wires 92 and 77, contact 45-45 of pressure responsive device P and wire 87 to wire 82. If, however, the pressure in the righthand end of cylinder 4 exceeds forty pounds per square inch when contact opens, the branch just traced for the circuit for valve V will be open at contact 4545 of pressure responsive device and valve V will therefore become deenergized. The fluid pressure which had previously been admitted to the right-hand end of cylinder 4 will then expand, and piston 5 will therefore continue to move toward the left under these conditions until contact 8637 of circuit con troller S becomes closed. WVhen this happens, if contact 45-45 of pressure responsive device P is then closed, as will be the case if the pressure in the right-hand end of cylinder 4 exceeds fifty pounds per square inch, another circuit for valve V will be completed, and current will flow from battery B through line wire 56, wires 57 and 58, winding 24 of valve V wires 59 and 81, contact 3637 of circuit controller S wires 80 and 88, contact 4545 of pressureresponsive device P wires 87 and 82, asymmetric unit 83 in its. low resistance direction, wire 84, line wire 67, wire 85, contact 4649 of lever L, and wire 86 back to battery B. Valve V will therefore become energized and will exhaust fluid from the righ -hand end of cylinder 4 until the pressure in this end of the cylinder has been reduced to fifty pounds per square inch, whereupon contact 45-45 of pressure responsive device 1 will open and will deenergize valve V It will be apparent, therefore, that when lever L occupies its 79 position, the piston 5 is forced toward the left-hand end of cylinder 4, and is held against auxiliary piston 6, by fluid under a pressure of between forty and fifty pounds per square inch.

If the operator moves lever L to its p position, a circuit is completed for valve V from battery B through line wire 56, wires 57, 58 and 72, winding 24 of valve V wires 71,79 and 92, contact 4243 of circuit controller S line wire 89, wire 90, contact 4650 of lever L, and wire 86 back to battery B. Valve V therefore becomes energized and admits fluid at full-line pressure to the right hand end of cylinder 4 to drive piston 5 toward the left and the braking apparatus 7 toward its effective position. Shortly after piston 5 starts to move, the circuit previously traced for valve V becomes closed at contact ESQ-33 of circuit controller S and valve V therefore becomes energized and admits fluid pressure to the lefthand end of cylinder 4 to hold piston 6 in its projected position. As pointed out hereinbefore, contact 4243 of circuit controller S remains closed until piston 5 has moved past the position at which it engages the auxiliary piston 6 when the auxiliary piston occupies its projected position, and it will be apparent, therefore, that under these conditions, valve V will remain energized so that piston 5 Will be held against piston 6 by full-line pressure.

If it is desired to apply still higher braking forces, the operator moves lever L to its p position, thereby opening contact 46*55 of circuit controller L, and closing contacts 46-51 and 46-53. When contact 46-51 of lever L is closed, a circuit is completed .for valve V which is similar to the circuit which is closed for valve V when lever L occupies its 10 position except that this latter circuit includes contact 4651 of lever L and wire 91 instead of contact 4650 of lever L and wire 90. Piston 5 is therefore moved toward the left by full-line pressure. Furthermore,

as soon as contact 3435 of, circuit controller S becomes closed, a circuit is completed for valve V and current flows from battery B through line wire 56, wire 57, winding 24 of valve V wire 94, contact 3435 of circuit controller S line wire 95,-contact 52*53 of lever L, and wire 86 back to battery B. Valve V therefore becomes energized, and vents the left-hand end ofcylinder 4 to at niosphere so that pistons 5.and 6 now move toward their extreme left-hand positions. It should be noted, however, that due to the throttling restriction 27 in the pipe 26, the rate at which fluid can escape from the lefthand end of cylinder 4 during this move ment of piston 6 is limited to a value which causes momentary compression of the fluid which remains in the cylinder between the piston and the adjacent end of the cylinder, thereby cushioning the action of the entire apparatus. As soon as piston 5 has moved past the position at which it normally engages the auxiliary piston 6 when the auxiliary piston occupies its projected position, contact 42-43 of circuit controller S opens and interrupts the circuit which waspreviously closed for valve V at this contact, and valve V therefore becomes deenergized and cuts off the supply of fluid to the right: hand end of the cylinder. The fluid which has already been supplied to the right-hand end of the cylinder then expands, and piston 5 therefore continues to move toward the left until contact 4243 of circuit controller S becomes closed. If the pressure in the righthand end of cylinder 4 then exceeds fifty pounds per square inch, a circuit will be completed for valve V over which current flows from battery B through line wire 56, wires 57 and 58, winding 24 of valve V wires 59 and 81, contact 3637 of circuit controller S wires 80 and 88, contact 4545 of pressure responsive device P wire 87, contact 42-43' of circuit controller S, line wire 89, wire 91, contact 4651 of lever L, and wire 86 back to battery B. Valve V will therefore become energized and will vent fluid from the right-hand end of cylinder 4 until the pressure in this end of the cylinder decreases below fifty pounds per square inch. If, however, the pressure in the right-hand end of cylinder 4 is below forty pounds per square inch when contact 4243 of circuit controller S becomes closed, a branch for the circuit over which valve V initially became energized when lever L was first moved to its 79 position, will be completed at contact 4545 of pressure responsive deviceP, this branch passing from wire 92 through wire 77, contact 4545 of pressure responsive device P wire 87, and contact 42 43 of circuit con troller S to line wire 89. Valve V will therefore again become energized and will admit fluid to the right-hand end of cylinder 4 until the pressure in this end of the cylinder exceeds forty pounds per square inch, at which time contact 4545 will open and deenergize valve V It will be apparent, therefore, that with the apparatus constructed in the manner here shown, when lever L occupies its 19 position, piston 5 is held in its extreme left-hand position by fluid at a pressure of between forty and fifty pounds per square inch. The parts are so proportioned that when piston 5 occupies its extreme left-hand position, lever 9 is moved to the position in which the toggle of which it forms a part is almost on dead-center. When the parts occupy these positions, the reaction of the wheels which is transmitted back to piston 5 from the braking bars while the braking bars are engaging car wheels of ordinary width, is insufficient to move the piston toward the right, and the entire forces exerted by the springs 17 18, 19 and 20 of the resilient connections are available to hold the braking bars against the car wheels. However, if a locomotive having wheels which are thicker than car wheels, is run through the braking apparatus, the excessive pressure exerted by the thick wheels against the braking bars, will overcome the resistance offered by piston 5, under these conditions, and piston 5 will move toward the right, thereby avoiding the excessive strains which would be present in the retarder if this move ment of the piston did not take place.

Itshould be observed that after the operator moves the lever L from a position corresponding to a higher braking force to a po sition corresponding to a lower braking force, the apparatus immediately and automatically reduces the braking pressure to a value corresponding to the new position of the lever in a manner which will be appar ent from the drawing without tracing the sequence of operation in detail.

In order to restore the apparatus to its open or ineffective position from its closed or efiective position, the operator moves lever L to its p position in which it is illustrated in the drawing, thereby closing contacts 46-47 and 4652 of lever L. The closing of contact 4647 of lever L under these conditions completes a circuit for valve V over which current flows from battery B through line wire 56, winding 24 of valve V wire 7 5, contact 3233 of circuit controller S wire 74, contact 4545 of pressure responsive device P wire 73, line wire 63, wire 64, contact 4647 of lever L, and wire 86 back to battery B. Valve V therefore becomes energized and admits fluid pressure to the lefthand end of cylinder 4, so that the auxiliary piston 6 is moved to its projected position in which it is illustrated in the drawings. The closing of contact 4652 of lever L under these conditions completes a circuit for valve V which is similar to that previously described for this valve in connection with position p of the lever, except that this circuit now includes contact 4652 of lever L instead of contact 4653. Valve V therefore becomes energized, and since valve V is energized, fluid pressure is admitted to pipe 28, and hence to the region between the pistons 5 and 6. Furthermore, the closing of contact 4647 of lever L under these conditions also completes the circuit previously traced for valve V and valve V therefore becomes energized to disconnect pipe 28 from atmosphere and to connect pipe 29 with atmosphere. When pipe 29 is connected with atmosphere, the pressure in the right-hand end of cylinder 4 is exhausted, and the pressure between the pistons 5 and 6 therefore moves piston 5 toward the right to restore the braking apparatus to its open or ineifective position in which it is illustrated in the drawing. If the pressure in the region of cylinder 4 between the pistons 5 and 6 exceeds thirty pounds per square inch during the movement of piston 5 toward the right, contact 45-45 of pressure responsive device P will open and will interrupt the circuit for valve V including this contact. Valve V will, there fore, become deenergized, and will cut off the supply of fluid pressure to the region between the auxiliary piston 6 and the adjacent end of the cylinder, and between the pistons 5 and 6. After the pressure has again dropped below thirty pounds per square inch, contact 4545 of pressure responsive device 1'' will again become closed to restore the circuit for valve V When piston 5 reaches its right-hand position, contact 3233 of circuit controller S and contact 3435 of -cir cuit controller S become opened, thereby opening the circuits for valves V and V respectively. The valves V and V therefore become deenergized, and the parts are then all restored to their normal conditions in which they are illustrated in the drawin When the valves V and V are deenergize the pipe 26 communicating with the lefthand end of cylinder 4 is blanked, and the fluid pressure which has already been supplied to the left-hand end of cylinder 4 is now trapped in cylinder 4 to hold the auxiiiary piston 6 in its projected positions.

One advantage of railway braking apparatus embodying my invention is that shortcircuiting of the contacts 4545 and 4545 of the pressure responsive devices P and P due, for example, to the collection of frost or moisture on these contacts, will not cause the retarder to close when the retardcr is in its open position.

Another advantage of railway braking ap paratus embodying my invention is that the control of the apparatus is effected over a minimum number of line wires by a minimum number of active contacts on the lever and with the use of a minimum number of asymmetric units.

Although I have herein shown and described only one form of railway braking apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

In combination, a railway braking bar located in the trackway and movable toward and away from a track rail into braking and non-braking positions, a cylinder, a first piston movable in said cylinder between one end of the cylinder and an intermediate point in the cylinder, a second piston operatively connected with said braking bar and movable in said cylinder between the other end of the cylinder and said first piston, a first winding for controlling the admission of fluid pressure to said cylinder between said first piston and the adjacent end of the cylinder, a second winding for controlling the admission of fluid pressure to said cylinder between said pistons, a third winding for controlling the exhaust of fluid pressure from the region of said cylinder between said pistons and between said second piston and the adjacent end of the cylinder, a fourth winding for controlling the admission of fluid pressure to said cylinder between said second piston and the adjacent end of the cylinder, a pair of line wires, means for reversibly supplying said line wires with current, two normally closed contacts responsive to the pressure in said cylinder between said second piston and the adjacent end of the cylinder and arranged to open successively as the pressure in said cylinder between said second piston and the adjacent end of the cylinder increases, two asymmetric units, means including one of said pressure responsive contacts and one of said asymmetric units for supplying said fourth winding with current from said line wires when and only when said line wires are supplied with current of one polarity, means including the other pressure responsive contact and the other line wire for supplying said fourth winding with current from said line wires when and only when said line wires are supplied with current of the other polarity, means controlled by said second piston for sho-rt-circuiting said contacts when and only when said braking bar is in its nonbra-king position; and means for selectively supplying said first, second and third windings with current.

In testimony whereof I affix my signature.

JOHN WV. LIVINGSTON. 

